The structure of a ground effect or air cushion (ACV) vehicle identifies the metallic assembly which on the one hand supports the superstructures, motor elements and payload and which on the other hand is supported at least in flight by the air cushion/cushions. In average tonnage ACV's of the type mentioned above, the said structure generally comprises an essentially rectangular platform supporting one or more longitudinal caissons or compartments, often symmetrical with reference to the long axis of the apparatus, inside which caissons it may be convenient to seat the heavy vehicles being transported. The platform is constituted for example by a rectangular reticulated grid formed of a plurality of longitudinal beams or girders which cross a plurality of transverse beams or cross girders supporting the floors. A certain volume of the said reticulated grid, generally at the periphery in order not to interfere with the air supply ducts for the cushion/cushions, is designed to ensure to buoyancy of the vehicle. The caissons are made of stiffened sheets assembled along four longitudinal ribs, and they bear on a plurality of transverse frames.
In the case of a single longitudinal caisson on the axis of the apparatus, such a structure is analogous to that of an airplane, the caisson resembling the fuselage, and the platform being analogous to wings running all along the fuselage. In longitudinal flexion the general stresses are accepted to major part by the central caisson. In transverse flexion they are accepted essentially by the platform, and in torsion, caisson and platform in varying degrees contribute to the total strength. On the other hand, local stresses on the floors due to the rolling loads that are transported are considerable. Consequently a structure of this kind presents two problems, one relating to connection of the caisson and platform, the other concerning the frame system of the platform.
So far as the connection of the caisson and the platform are concerned, two extreme solutions can first be imagined. The first consists in providing a central caisson that rises over the whole height of the structure. The modulus of inertia of longitudinal flexion is good, but the platform is actually split into two semi-platforms, the transverse stresses causing the connections of each half platform and the caisson to work independently, which makes it necessary to reinforce these connections and complicate them. Moreover, a floor that is sufficiently stong to receive the heavy vehicles must be provided horizontally in the caisson, which increases the weight of the structure. The second solution consists in having the caisson rest on the platform. The platform remains integral and without any break in continuity, which is favorable insofar as propagation of transverse and diagonal stresses is concerned. The lower part of the caisson can serve directly as support framing or armor for the heavy vehicle floor. However, the modulus of inertia of the caisson is clearly less good, the reduction of the value of the modulus has to be compensated by a reinforcement of the caisson, which substantially adds to the weight of the structure.
An object of the present convention consists in provision of a structure wherein the caisson and the platform are coupled so as to present the advantage of the two above solutions without their drawbacks, which allows production of an overall structure that is lighter.
As far as the frame system of the platform is concerned, what must be provided essentially is an arrangement of contiguous squares, to get a relatively undeformable platform, both for its production and servicing, and for hoisting.
An object of the present invention consists specifically in providing a relatively light platform while ensuring a certain indeformability.
According to a characteristic of the present invention, a ground effect vehicle structure is provided comprising a caisson and a platform, in which the caisson has its two lower longitudinal edges rigidly connected respectively to two principal or main girders in a grid of the platform, the crosswise portions between the two said main girders and slightly to either side thereof being reinforced.
According to another characteristic of the invention, certain girders of the platform, including the main girders, are lattice girders, while the others are ladder-structure girders, including the girder or girders between the two principal girders, the distribution of lattice girders and ladder girders being symmetrical with reference to the long axis of the vehicle.
Other characteristics of the present invention will become clear upon perusal of the following description of an example of embodiment, said description being presented with reference to the attached drawings.